Just for the record, medicines containing pseudoephedrine in combination with other drugs are available in Singapore, but it's not sold in pure form. No problems with importing it though.

The official list of medicines that may not be imported into Singapore without explicit advance permission is here:

http://www.hsa.gov.sg/publish/hsapor...edication.html

This is mostly heavy-duty painkillers and sedatives (incl. Valium!), and bringing along a prescription won't cut it.